Two stage electrolytic and chemical process for alpha-olefin conversion to aliphaticacids



United States Patent Ofi 3,419,483 Patented Dec. 31, 1968 ice 3,419,483 TWO STAGE ELECTROLYTIC AND CHEMICAL PROCESS FOR ALPHA-OLEFIN CONVERSION TO ALIPHATIC ACIDS Gunner E. Nelson, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Jan. 28, 1964, Ser. No. 340,782 5 Claims. (Cl. 204-79) ABSTRACT OF THE DISCLOSURE Acids are produced from alpha olefins without chain length degradation by performing a two stage oxidation, the first in an electrolytic stage, the second stage selective to completion of the initial oxidation to the acid state.

This invention relates to the production of aliphatic acids and in particular to the production of such by the oxidation of alpha olefins accomplished in part by elec trolytic process and in part by chemical process.

One attractive source of possible raw materials for the production of aliphatic acids is the class of materials known as alpha olefins. Although these materials are readily available and comparatively inexpensive, a practical obstacle exists to the widespread utilization thereof in the production of the aliphatic acids because of the expense involved in the conventional forms of chemical conversion from the olefin to the acid. Of potential interest in this connection is conversion by processes which are at least in part non-chemical. In this area British Patent 609,594 describes a process involving electrolytic conversion of gaseous olefins to acids. Various practical considerations relating to this process suggest the desirability for substantial improvement. Although not suggested by the foregoing British patent, a two-step operation in which the olefins are first converted to some intermediate material such aldehydes which in turn are converted to the end product desired, namely the aliphatic acids, is advantageous. The first of these steps, the conversion of the olefin to an intermediate product, is somewhat expensive and difficult to perform chemically. However the second step of the process, namely the oxidation of the intermediate product to the aliphatic acid, is a step which is readily and inexpensively accomplished chemically and which, although it could be performed electrolytically, involves considerably more expense in so doing. According to the process of the foregoing British patent the entire conversion is accomplished electrolytically without any intermediate product formation. Thus a new overall process terminating at least a substantial portion of the electrolytic oxidation with the production of the intermediate product leaving a substantial portion of the oxidation to be accomplished chemically ofiers substantial promise.

It is accOrdingly an object of the present invention to provide a combined electrolytic and chemical conversion process for the production of aliphatic acids from alpha olefins.

Another object of the present invention is to provide a process involving the controlled electrolytic conversion of alpha olefins to an intermediate product which may be subsequently converted chemically to the aliphatic acid.

Another object of the present invention is to provide an electrolytic process for the conversion of alpha olefins to a product intermediate the olefin and the aliphatic acid.

Another object of the present invention is to provide an electrolytic conversion process whereby a substantial amount of materials intermediate the alpha olefins and the aliphatic acids may be prepared wherein the alpha olefins involved are preferably in the range of from about 10 to about 15 carbon atoms per molecule.

Another object of the present invention is to provide a process for the electrolytic oxidation of alpha olefins in the liquid phase.

Another object of the present invention is to provide a process for the controlled electrolytic oxidation of alpha olefins having from about 10 to about 15 carbon atoms per molecule to an intermediate product between the olefin and the aliphatic acid which intermediate product can be readily oxidized chemically to the corresponding aliphatic acid.

Other and further objects and features of the present invention will become apparent on a careful consideration of the following detailed description of the present invention.

In accordance with the basic teachings of the present invention, controlled oxidation of alpha olefins having up to approximately 30 carbon atoms per molecule, preferably 10 to 15 carbon atoms per molecule, and typically decene-l, is obtained by electrolysis of the olefin in an acid electrolyte while the olefin is in the liquid phase, such liquid phase being maintained typically by substantial agitation of the electrolyte-olefin mixture, assisted by surface active agents and the like. Experimental work has established desired ranges of electrolyte composition and concentration as well as electrolytic current density and reaction duration. Optimization through the selection of various promoters and catalysts, anode materials, and temperatures has been made.

In British Patent 609,594 propylene is introduced into an electrolytic cell as a cloud of fine bubbles. The electrolysis is described as being carried to completion, namely the production of the acid which is the desired result. As a practical matter it appears that vapor phase oxidation requires such large reactor volume to achieve any quantity of olefin content as to virtually make it impractical to attempt to carry the reaction only part way and in fact there is no suggestion that such is even desirable or accomplished. The drawback of this prior art manipulation is that, while it accomplishes the difiicult chemical oxidation of the olefin it unavoidably wastes electrical energy in performing the complete oxidation electrolytically which latter step is an operation that can be accomplished chemically at much less expense. It has been found that by control of the electrolysis conditions to insure that the olefin being subjected to electrolysis is in the liquid phase, that it is possible to provide such a vast increase in the olefin concentration in the electrolyte as to make it possible to stop the electrolysis after a substantial portion of the intermediate product has been formed but before the intermediate product has been completely converted to the aliphatic acid. It is then possible to provide a second step in the process involving the chemical oxidation of the intermediate product, the result being the production of the aliphatic acid at a considerable saving over wholly electrolytic or Wholly chemical conversion processes.

The performance of the reaction with the lower carbon number olefins such as those having 6 or less carbon atoms per molecule will in general require the use of pressure vessels or reduced reaction temperatures. In general, however it has been found that reaction temperatures for a typical olefin, decene-l, are preferably in the range of 20 to 30 C. so that regardless of the materials used it will be found that optimization results with certain temperature ranges for the reaction.

Electrolysis as performed in accordance with the fore going requires a suitable electrolyte. Strong acid electrolytes such as sulfuric are preferred, usable concentrations ranging from to 60 weight percent with preferred concentrations being of the order of 15 to 20 percent. Olefins in general are not particularly miscible with such electrolytes which means that the best situation that usually can be obtained is a mixture of droplets of olefin within the electrolyte requiring continuous agitation and the like. It has been found that some improvement along these lines results from the use of surface active agents such as benzene sulfonic acid and benzene disulfonic acid used in proportion of from about 0.1 to 1.0 weight percent based upon the electrolyte.

Current densities involved in the electrolytic action affect operation and results to a marked degree. In general there is a correlation between optimum current density and concentration of the electrolyte as well as the composition of the electrolyte. Usable current densities range up to about 50 amperes per square foot of anode area with preferable current ranges being from 4.3 to 14.4 amperes per square foot of anode area with sulfuric acid electrolyte concentration of 15 to 20 percent. In general it may be stated that the lower current densities favor high yields of the intermediate material such as the aldehyde and in general a more efficient conversion to the aldehyde in proportion to the amount of electrical power consumed. Again in general, the higher current densities result in an increased production of ketones and esters which intermediate materials are not particularly suitable for simple chemical oxidation to the acids, and hence these higher densities are less efficient both on the basis of production of the desired aldehydes and on utilization of electrical power.

Another important factor in the efiicient electrolytic conversion is electrode material. Although several electrode compositions such as mercury, lead oxide, a leadmercury and amalgam, various mercury-carbon structures, and the like have produced electrolytic conversion, in general simple lead electrodes are preferable and it has been found that electrodes experience improvement after a moderate amount of aging. Although the anode electrode exerts a substantial influence upon the electrolytic oxidation process, the effect of the cathode electrode is relatively minor and virtually any material that is a conductor not adversely affected by the electrolyte involved will suffice. Typically even a metal wire is adequate.

The electrolysis occurs principally in the region of the anode electrode and olefin is neither desired nor helpful in the region of the cathode electrode since it may actually interfere with the conductivity of the electrolyte in that region. Thus it has been found advantageous to place the two electrodes in separate chambers interconnected by means of a suitable restricted flow path to minimize the entry of olefin into the cathode chamber but yet not seriously interfere with the conductivity of the cell, such restriction being provided typically by means of a glass frit of suitable proportions. Typically for operating conditions such as those described in the following paragraphs a glass frit of low porosity is suitable.

Although the electrolytic conversion will take place without catalysts it has been found that the presence of suitable catalysts such as a mercury salt typified as the oxide or sulfate present in the proportion of about 0.1 to 10 grams of the salt per 100 grams of electrolyte will produce improved results. A preferred catalyst proportion range is from about 1 to 2 grams mercuric oxide per 100 grams of electrolyte.

A further factor worthy of note is the concentration of olefin present in relation to the electrolyte. There is an optimum concentration of olefin between the extremes on the one hand of such a low olefin concentration as to approach the poorly controllable low ratios used in the vapor phase oxidation of the foregoing British patent, and on the other hand of an upper limit on olefin concentration wherein the fluid material between the electrodes begins to predominate in olefin rather than electrolyte, adversely affecting conductivity. Therefore a general range of olefin concentration from about 1 to about 25 weight percent based on the electrolyte is usable, with a preferred range being from about 2.5 to about 10 percent. A typical concentration of 5 percent was selected as a starting point in a determination of the usable ranges of the many other variables involved as outlined in the foregoing paragraphs.

For the following examples the apparatus employed a one liter three-necked flask having a side arm sealed in near the bottom. This side arm was basically a horizontal tube arrangement leading to a vertical cathode chamber. The side arm and the vertical cathode chamber were each of 30 millimeters diameter, and the glass frit restrictive device mentioned in the foregoing was disposed within the horizontal connecting tube. A stirring device is placed in one of the necks of the flask and the anode electrode is introduced in a second neck. Typically the anode configuration is a bar of lead measuring approximately 1.5 by 3 inches providing a total contact area with the electrolyte of approximately 10 square inches. Electrolyte and olefins are introduced into the flask through the third neck by means of which samples may be removed for analysis. In performing each run 650 milliliters of electrolyte. 37 grams of decene-l, the indicated amount of catalyst and promoter were added, the current adjusted to the desired amount, temperature set to the desired amount or merely read depending upon the nature of the runs and the current flow was continued for the indicated amount of time. Yields were calculated on the basis of percent of decanoic acid and decyl aldehyde produced based upon the amount of decene-l converted which latter quantity was obtained by analyzing the reaction product mixture for decene-l and comparing it to the decene-l that was introduced initially. In Run 39 the amount of decene-l charged to the reactor was 100 grams instead of 37.5. In this run decanoic acid was not formed and a higher than normal ratio of 'ketone to aldehyde was produced,

Equally desirable results are obtained with other olefins such as octene-l, dodecene-l, and octadecene-l substituted for the decene-l of Runs l-39.

Elee- Catalyst, trolyte, Current Temp, Ampere Promoter, Yield weight Example Anode weight density, Voltage 0. hours weight percent percent, Amp/ft. percent Acid Aldehyde HgO TABLE-Continued Elec- Catalyst, trolyte, Current Temp., Ampere Promoter, Yield weight Example Anode weight density, Voltage 0. hours weight percent percent, Amp/ft. percent Acid Aldehyde HgO 40 14.5 5.0 26 17. 5 10.2 27. 1 05 2O 21. 6 6. 7 30 8. 5 4. 3 30. 4 05 40 21. 6 6. 7 35 9. O 17. 5 26. 4 05 60 21. 6 6. 8 45 9.0 37. 8 25.6 05 15 11.5 4. 7 24 17.6 .114 13811.... 26.5 47.4 .05 15 11.5 4.5 23 16.0 1.0 BSA 36.1 43.9 .05 15 11.5 4. 5 23 14.4 114 BDSA 33.0 41. 2 05 15 11. 5 4. 5 23 14.4 1.0 BDSA 43.0 50. 7 .05 15 11.5 4. 7 24 16. 8 34. 8 46. 8 .05 20 14. 4 4. 7 25 18. 39. 4 37. 2 055 20 14. 4 4. 7 24 20 46. 8 41. 1 11 20 14. 4 4. 7 24 18 44. 3 47. 1 22 20 14. 4 4.7 24 17 21. 7 23.1 44 20 14. 4 4. 7 15 17 62.0 20. 1 .11 20 14.4 4. 7 45 17 22.1 31. 9 11 14.4 18. 25 17 Trace 20. 5 11 20 1.44 3.1 26 2. 4 5 13.6 .11 20 14.4 9.0 25 17 16. 9 17. 9 11 2O 14. 4 5. 1 27 17 16. 9 34. 7 11 20 14.4 5. 2 27 17 13. 2 l4. 6 20 28. 8 8. 3 28 34 32. 4 25. 6 20 14. 4 5. 0 25 27 1 5% H SO S317. HaBOa.

In Example I the intermediate product was oxidized to produce decanoic acid by exposure to oxygen.

Having thus described the process of this invention and the products thereby produced, it is not intended that it be limited except as set forth in the following claims.

What is claimed is:

1. The process for converting u-olefins into saturated aliphatic acids comprising:

electrolyzing the a-olefin in the liquid phase to an intermediate product in an electrolytic cell in the presence of an aqueous electrolyte and then chemically oxidizing the intermediate product to the aliphatic acid.

2. The process for converting u-OlefiIlS having up to about 30 carbon atoms per molecule to the corresponding aliphatic acid comprising electrolyzing in the olefin in an electrolytic cell in the liquid phase in a sulfuric acid aqueous electrolyte of about 5 to about 60 weight percent concentration with HgO catalyst present from about 0.1 to weight percent of the electrolyte, a sulfonic acid of benzene present from about 0.1 to about 1.0 weight percent of the electrolyte, the initial olefin concentration being from about 1 to about 25 weight percent of the electrolyte, at a temperature from about to 30 C., at a current density at a lead electrode of from, about 5 to about 50 amperes per square inch with from about 2 to about 50 ampere hours, and then chemically oxidizing the electrolysis product with oxygen.

3. The process for converting lit-Olefin having up to about 30 carbon atoms per molecule to the corresponding aliphatic acid comprising electrolyzing the olefin in an electrolytic cell in the liquid phase in a sulfuric acid aqueous electrolyte of about 5 to about 60 weight percent concentration with HgO catalyst present from about 0.1 to 10 weight percent of the electrolyte, a sulfonic acid of benzene present from about 0.1 to about 1.0 weight percent of the electrolyte, the initial olefin concentration being from about 2 to about 5 weight percent of the electrolyte, at a temperature from about 20 to 30 C., at a current density at a lead electrode of from about 5 to about 50 amperes per square inch with from about 2 to about 50 ampere hours, and then chemically oxidizing the electrolysis product with oxygen.

4. The process for converting a-OlCfiIlS having from about 10 to about 15 carbon atoms per molecule to the corresponding aliphatic acid comprising, electrolyzing the olefin in an electrolytic cell in the liquid phase in a sulfuric acid aqueous electrolyte of about 20 to about 40 weight percent concentation with HgO catalyst present from about 0.1 to 2 weight percent of the electrolyte, a sulfonic acid of benzene present from about 0.1 to about 1.0 weight percent of the electrolyte, at a temperature from about 20 to 30 C., at a current density at a lead electrode of from about 10 to about 25 amperes per square inch with from about 10 to about 25 ampere hours, and then chemically oxidizing the electrolysis product with oxygen.

5. In the process of preparing saturated high molecular weight straight-chain aliphatic acids having from about 10 to about 15 carbon atoms per molecule from the corresponding alpha olefins the improvement according to which the olefins are anodically oxidized to a mixture containing the desired acid and its corresponding aldehyde, the combined mol content of the acid and the aldehyde being not more than about 93.7 percent, and then exposing the mixture to oxygen to complete the oxidation to acids.

References Cited Chemistry, Boston, Allyn and Bacon, Inc., 1959, pp. 622 and 628-629.

JOHN H. MACK, Primary Examiner. D. R. VALENTINE, Assistant Examiner.

US Cl. X.R. 

